This invention relates in general to techniques for physically moving a part in response to temperature variations in order to maintain accurate alignment and operation and, more particularly, to such techniques which provide a relatively large physical movement for a given temperature change.
There are a variety of types of systems which must operate properly over a relatively wide temperature range. In order for some of these systems to operate properly throughout the temperature range of interest, the position of a part therein must be adjusted physically with respect to other parts in response to temperature changes. One example is an optical assembly, in which it is often necessary to respond to temperature variations by adjusting the position of one optical component such as a lens in relation to other optical components, for example to maintain an accurate focus throughout the temperature range. Consequently, it is common in this type of optical assembly to provide some form of xe2x80x9cathermalizationxe2x80x9d compensation structure that will effect a progressive positional adjustment of the lenses in response to progressive variations in temperature.
Where the appropriate rate of relative movement is small, it is possible to provide a single compensation component which supports the moveable part (such as a lens) for movement relative to other parts, and which has a coefficient of thermal expansion (CTE) selected to effect relative movement between the parts at the appropriate rate in response to temperature changes.
Where a somewhat higher rate of relative movement is desired, more sophisticated compensation devices have been developed, including a xe2x80x9ctube-in-a-tubexe2x80x9d approach in which two tubes with different CTEs are provided in a nested arrangement, with the tubes fixedly coupled to each other at one end, and with each tube coupled at the other end to a respective one of the two parts that are to be subjected to relative movement. However, this tube-in-a-tube approach is not particularly physically compact in the direction of relative movement, especially as the required rate of relative movement increases. This can be obviated to some extent by concentrically nesting several pairs of these tubes. However, the resulting arrangement is physically complex and relatively large in size, and has a relatively large weight that is disadvantageous in certain applications such as an airborne or space-based application. A further disadvantage of this arrangement is that it has several tolerances in a radial direction which can cumulatively produce significant inaccuracy, and has several tolerances in an axial direction which can cumulatively produce significant inaccuracy.
In an attempt to overcome the drawbacks discussed above, a more recent known approach uses a series of cooperating wedge rings, an example of which is disclosed in McCrary U.S. Pat. No. 5,557,474. While this approach has been generally adequate for its intended purposes, it has not been satisfactory in all respects. In this regard, the various wedge parts have an inherent degree of looseness or play between them, which can lead to inaccuracies in their ability to effect relative positioning of other parts in response to temperature changes. Further, friction between sliding surfaces on the wedge rings can resist smooth sliding movement between these surfaces, thus giving the temperature compensation movement a somewhat non-linear or xe2x80x9csteppedxe2x80x9d effect. Still another consideration is that this known compensation mechanism has, in the direction of compensation movement, an overall physical dimension which is significantly larger than the space available in some types of systems.
From the foregoing it may be appreciated that a need has arisen for a method and apparatus for effecting relative movement of two parts in response to temperature changes, in a manner which avoids some or all of the disadvantages of the preexisting devices that have been discussed above. According to the present invention, a method and apparatus are provided to address this need, and involve a device with first and second members respectively having a first coefficient of thermal expansion and a second coefficient of thermal expansion greater than the first coefficient, the first member having first and second portions that are offset with respect to each other in a direction parallel to a compensation direction and also in a direction perpendicular to the compensation direction. The second member responds to a temperature change by cooperating with the first member so as to effect movement of the first portion relative to the second portion in a direction transverse to the compensation direction, in a manner changing a dimension of the device in a direction parallel to the compensation direction.